Copolymeric siloxanes and methods of preparing them



Patented Apr. 20, 1954 T COPOLYMERIC SILOXANES AND METHODS- OF PREPARING THEM William Herbert Daudt and Leslie Junior Tyler; Midland, Mich., assignors to Dow Gc'rnin: Gor poration, Midland, Mich.,- acorporation of Michigan No Drawing. Application September 13, 1950,

' Serial No. 184,720

3' Claims (Cl. Mll -448.2);

This inventicnrelates 20" copolymeric siloxanes containing SiOz;

In:- the commercial preparation of copolymeric siloxanes, particularly siloxane resins, the heretoforeemployed procedure has generally been to 5 and dried. The products thereby obtained range cohydrolyze and cocondense various hydrolyzable from viscous oils to thermoplastic resins, dependsilanes. In those copolymers containing unsub: ing upon the size of the organic groups and the stituted silicon it has been heretofore necessary ratio of organosilyl groups to silica. to employ aspecial procedure in order to obviate If desired, water-miscible solvents may be em 7 excessive gel formation. This gel formation is 10 ployed in order to increase the rate of the re-' undesirable since the gelsthemselves are not action. Suitable solvents include fatty'alcohols, usable. Heretofore, in commercial operations, dioxane, ketones, and water solublecarboxylic the only practicable procedure for incorporating acids. At times it is advisable toemploy-combiunsubstituted silicon in a siloxane resin has been nations of water-soluble and water-insoluble solthat of employing eithertetraalkoxysilanes or an 16 vents such as toluene; xylene, and ether. The alcoho1 hydrolysis medium which is equivalent to presence of a solvent is not necessaryto the reemploying a tetraalkoxysilane. action. I o

The applicants have found that unexpectedly The organosilicon compounds which are embeneficial materials are obtained when silanes or ployed in this invention are silanes of the formula siloxanes are reacted with a silica hydrosol, It 20 RnSiX4-n and siloxanes'of'the formula has been foundunexpectedly that not only does 1 R Sio the method produce materials which are completely soluble in organic solvents such as toluene, but also that the copolymers so formed are suor combinations thereof. In order to obtain the perior in many respects'to' copolymers produced desirable benefits of this invention, the organoby the cohydrolysis of organo silanes with silicon -silicon composition should be employed in tetrachloride or ethyl orthosilicate. amount sufficient that there is at least a total of It is an object of this. invention to provide a one moi of organosilyl groups per'mol of SiO2 in commercially feasible method for preparing sithe silica'liydr'osol. Preferably; theam'ount of si.- loxane-copolymers containing S102 which is more lane employed is at least 3 mols per mol of SiO'r; economical than heretofore known procedures. If less than an equimolar ratio is used, the prod- Another object is to prepare improved org'anouct obtained is undesirable. However, it has been siloxane cop'olymers which are superior" to those found that any amount of silane in excess of a 1 which are prepared by the cohydrolysis of hydroto 1 molar ratio maybe employed without delelyzable silanes. Other objects and advantages 85 teriously affecting'the reaction. will be apparent from the following description. The silanes and'siloxanes which are within the In accordance with this invention an organoscope of this invention and which are operative silicon composition composed of compounds of therein are those in which theR groups are alkyl, the-groupRnSiX i-n and mon'ocyclic aryl hydrocarbon, or halogenated R Sio 0 'monocyclic aryl hydrocarbon. At least per .1" cent of the total number of R groups are alkyl'. 2 The hydrolyzableradicals on the silanes are chlowhere R is alkyl, monocyclic aryl hydrocarbon, rine or alkoxy di als, a dl at d mo ocyc c a y hy X The silanes and siloxanes may be employed inis-fihlcfl'ne 0! y, aL d'n has avalu'e' from. lie 5 dividually or in mixture. In those cases in which 3,.the-averagedegree ofisubstitutionofsaid comchlorosilanes are-employed it is unnecessary .to DQSiBiOII beinglfiomll o R ups p silicon add any acid to the reaction mixture, since HCl atomand at. least. 50: percent of the Rgroups bewill be formed in situ. In such cases the chloroingalkyl is reacted'with. a silica hydrosol having silane may be added directly to a sodium silicate a pI-I of:less.than 5, inamount such. that there'is solution. In cases where alkoxy silanes and siat leastonemol. of organosilylgroupsper' mol of loxanes are employed it is necessary that thesil- I SiOz in the silica hydrosol. ica hydrosol contain sufiicient acid so that the It has been; found that reaction betweensilica pH thereof shall be less. than 5. Suitable acids hydrosols, silanes and/or siloxanes proceeds are hydrochloric, sulfuric, nitric, phosphoric, rapidly at 30 C. or aboveto produce copolymeric' benzenesulphonic, tri'cliloroacetic; and any other.

siloxanes. During the reaction the mixture is preferably thoroughly agitated. In general, an

emulsion forms which separates into two layers upon standing. The layers are then separated l and the'organosilic'on layer washed free of acid strong acid-L Any amount ofacid in excess of that 1 necessary to produce a PH of less than may be employed.

It is to be understood that any combination of any of the above organosilicon compounds can be employed, provided the degree of substitution of the mixture is between 2.1 and 3. Thus, the organosilicon composition is RsSiCl, RsSiOR, or (RaSi) 20, either alone or in combination or together with limited amounts of R2SiX2, RSiXi. RzSiO, and RsiOz z. Specific examples of individual compounds which are within the purview of this invention are trimethylchlorosilane, trimethylethoxysilane, trimethylisopropoxysilane, phenyldimethylchlorosilane, hexamethyldisiloxane, dimethylsiloxane, phenyltrichlorosilane, diethyltetramethyldisiloxane, tolylmethyldichlorosilane, methyltriethoxysilane, stearyltrichlorosilane, chlorophenyldimethylchlorosilane, monotolylsiloxane, and trifluorotolylmethyldichlorosilane.

The silica sols employed herein may be prepared in the usual manner, by neutralizing sodium silicate solution. As has been pointed out, this neutralization may be accomplished either by employing an acid or a chlorosilane. In the latter case, it is not necessary to add any additional acid to the reaction mixture. Whereas the silica sol of any concentration would react with the above defined organosilicon compounds under acid conditions, it is preferred for the purposes of this invention that the sol have a concentration of from 1 to 35 per cent by weight SiOz.

Under the above conditions, reaction between the organosilicon compounds and the silica of the hydrosol takes place to produce copolymers in which organosilyl groups are linked to the silicon of the S102 through oxygen atoms. The copolymers are uniquely useful for water-proofing applications, for anti-flotation of paint pigments, and for thickening dimethylsiloxane fluids. The present method makespossible the production of siloxane copolymers at a greatly reduced cost over the heretofore employed cohydrolytic method.

The following examples are illustrative only of the invention and should not be construed as limiting the scope thereof, which is particularly delineated in the appended claims.

Example 1 The silica sols employed in the following examples were all prepared from a sodium silicate solution containing 26.7 per cent by weight SiOz and 8.2 per cent by weight NazO and having the empirical formula Na2O'3fiSiO2. The specific gravity of the solution was 1.365.

90.5 ml. of the above sodium silicate solution was diluted with 500 ml. of water, and 45 ml. of trimethylchlorosilane was added all at once to neutralize the sodium. An additional 115 ml. of trimethylchlorosilane was added portion-wise with agitation. A thick emulsion was obtained which coagulated to give a powdery material. The mixture was filtered and the powder was washed until neutral, dried, and extracted with chloroform. There was obtained a soluble fraction which melted at 140 C. to 160 C. and had a methyl to silicon ratio of 1.48. After extraction, an insoluble portion remained which had a methyl to silicon ratio of 1.13- a Example 2 v ml. of concentrated HCl to give an acidic sol containing .09 g. of $102 per ml. 50 ml. of the acid sol was diluted with 25 ml. of ethanol and there was added thereto all at once 25 ml. of dimethylphenylchlorosilane. The mixture. was agitated and a temperature rise was noted. The mixture formed an emulsion which separated into an oily precipitate and an aqueous phase. The oily precipitate was filtered, washed with water, and ex tracted with hot alcohol. The extract was concentrated to give a viscous soluble material which softened upon warming, and which was" a copolymer of phenyldimethylsiloxane and SiOz.

Example 3 The standard sodium silicate solution of Example 1 was diluted with 250 ml. of water, and

aqueous phase. and the organic layer was washed with water until 125 ml. of HCl was added thereto. To the acid silica sol was added a mixture of 1000 ml. hexamethyldisiloxane and 250 ml. of ethanol. The

entire mixture was thoroughly agitated and after,

ten minutes an emulsion formed. The emulsion soon separated into an organic phase and an The two layers were separated neutral and dried over calcium chloride. The alcohol and excess hexamethyldisiloxane were removed to give a white, friable, powdery resin.

This material was completely soluble in solvents such as toluene and xylene. It was a copolymer of trimethylsiloxane and SiOz.

Example 4 A silica hydrosol containing 0.18 g. of S102 per ml. was prepared by treating ml. of the sodium silicate solution of Example 1 with 25 ml. of

water and 25 ml. of concentrated HCl. 100 ml.

which separated to give two clear layers.

solvent was removed to give a soluble, thermo- "plastic resin which was a copolymer of trimethyl siloxane and S102.

Example 5 100 ml. of ethyldimethylchlorosilane was hydro- 1 lyzed by shaking with 500 ml. of water. hydrolyzate was added to 100 ml. of an acid silica hydrosol having a density of .18 g. of SiO2 perm The hydrosol was I aprepared as shown in Example 4. Themixture; was agitated and an emulsion formed which broke ml. and 250 ml. of ethanol.

to give two clear phases. The organic phase was washed until neutral, and upon removal of the solvent a soluble, white, powdery material was This was a copolymer of ethyldimethylsiloxane and Example 6 g. of SiOz per ml. was prepared as shown in Ex- 25 ml. of the above sodium silicate solution was diluted with 50 ml. of water and then added to 25 ample 4. The sol was diluted with 50 m1. of

ethanol and mixed with 25 m1. of hexamethyldisiloxane and 25 ml. of cyclic dimethylsiloxane. The mixture was agitated, whereupon an emul ."SiOn formed which separated into two layers. The organic layer was washed with water until neutral and the solvent was removed therefrom to give a solid, friable material which was soluble in organic solvents such as toluene, and was a copolymer of trimethylsiloxane, dimethylsiloxanej and S102.

The mixture was The I Example 7 A silica hydrosol containing .18 g. 0! $02 per ml. was prepared in accordance with the method of Example 4. 300 ml. of the acid sol was diluted with 150 ml. of ethanol and cooled to C. The sol was added to 100 ml. of toluene and stirred vigorously durin 10 minutes while a mixture of 100 g. of trimethylchlorosilane and 50 g. of phenyltrichlorosilane was added. An emulsion formed and the mixture became quite warm. The mixture was stirred for two hours and then allowed to stand overnight. The upper layer which separated was removed, washed neutral, and the solvent was evaporated. There was obtained a clear viscous fluid which was a copolymer of trimethylsiloxane, monophenylsiloxane, and SiOz.

Example 8 When the silica sol of Example 7 is reacted with trimethylchlorosilane and stearyltrichlorosilane in the manner and proportions shown in that example, a viscous fluid which is a copolymer of trimethylsiloxane, monostearylsiloxane, and SiOz is obtained.

Example 9 100 ml. of a silica hydrosol having .18 g. of SiOz per ml. was prepared in accordance with Example 4 and was diluted with 100 m1. of ethanol and mixed with 50 ml. of bischlorophenyltetramethyldisiloxane. The mixture was agitated, whereupon an emulsion formed which separated into two layers. The organic layer was washed with water until neutral, and upon removal of the solvent a copolymeric siloxane containing chlorophenyldimethylsiloxane and SiO2 was obtained.

That which is claimed is:

1. A method of preparing copolymeric siloxanes which comprises reacting an organo silicon composition composed of compounds selected from the group consisting of RnSiX4-n and where R is selected from the group consisting of alkyl, monocyclic aryl hydrocarbon, and halogenated monocyclic aryl hydrocarbon radicals.

X is selected from the group consisting of ch10- rine and alkoxy radicals, and n has a value from 1 to 3, the average degree of substitution of said composition being from 2.1 to 3 R groups per silicon atom, and at least per cent of the R groups being alkyl, with a silica hydrosol having a pH of less than 5 in amount such that there is at least one mol of organosilyl groups per mol of SiOz in the silica hydrosol, said silica hydrosol having been prepared by reacting a water-soluble alkali metal silicate with an acid.

2. The method in accordance with claim 1 wherein the concentration of the hydrosol is from 1 to 35 per cent by weight S102.

3. A method of preparing copolymeric siloxanes which comprises reacting a methyl silicon composition selected from the group consisting of (CH3)1lSiX4-n and where X is selected from the group consisting of chlorine and alkoxy radicals and n has a value from 1 to 3, there being on the average from 2.1 to 3 methyl groups per silicon atom, with a silica hydrosol having a pH of less than 5 and a concentration of from 1 to 35 per cent by weight 8102, said methyl silicon composition being employed in amount such that there is at least one mol of the methyl silyl groups per mol of SiOz in the silica hydrosol, said silica hydrosol having been prepared by reacting a water-soluble alkali metal silicate with an acid.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,441,320 Hyde May 11, 1948 2,441,422 Krieble et a1 May 11, 1948 2,458,944 Hyde Jan. 11, 1949 2,486,162 Hyde Oct. 25, 1949 2,521,390 Meadowcroft Sept. 5, 1950 2,562,953 Rust et a1 Aug. '7, 1951 OTHER REFERENCES Shaw et al., The Industrial Chemist, March 1945, pp. to 135. 

1. A METHOD OF PREPARING COPOLYMERIC SILOXANES WHICH COMPRISES REACTING AN ORGANO SILICON COMPOSITION COMPOSED OF COMPOUNDS SELECTED FROM THE GROUP CONSISTING OF RNSIX4-N AND 